Various biological fluid treatment processes are based on disintegration of unwanted bio-degradable substances from the fluid by microorganisms growing in the fluid. Such biological fluid treatment processes may utilize biomass carriers for growing the microorganism. For example, the biomass carriers in liquid treatment are usually relatively small elements having a density close to water density so as to be kept suspended in the water. The larger the surface area of a biomass carrier available for the development of microorganisms per volume of the biomass carrier the more efficient is the removal of the bio-degradable substances. Consequently, biomass carriers have usually a complex design with multiple pores. The carrier's manufacturing cost depends mostly on the raw material quantity required to support the high surface area. Moreover, the carrier structure is very volumetric enclosing high void volume, influencing the shipment costs.